1. Field of the Invention
This invention relates to a method for coating substrates with a copolymer of ethylene with chlorotrifluoroethylene, tetrafluoroethylene or mixtures thereof.
2. Discussion of the Prior Art
Coating compositions of copolymers of ethylene with chlorotrifluoroethylene or tetrafluoroethylene are well known in the art. These copolymers have outstanding mechanical, electrical and chemical properties at high temperatures. For example, about equimolar ethylene-chlorotrifluoroethylene copolymers are resistant to attack by most organic solvents at ambient, as well as elevated temperatures. They are also insoluble in acids and bases, including fuming nitric acid, possess high tensile strength and have melting points above about 200.degree. C. Such copolymers are suitable for making such useful articles as valves, gaskets, pipes, wire insulation, sheets, films, etc.
These copolymers have met with limited commercial success owing to certain disadvantageous properties. For example, while these copolymers were known to have melting points as high as about 300.degree. C., they could not be used at high temperatures, even far below their melting points, in applications requiring strength owing to deterioration of the mechanical properties of the copolymer. For, example, when used as wire coating, the copolymer became brittle at about 200.degree. C., and cracked under relatively low stress leaving the wire exposed.
Attempts have been made to overcome such disadvantages. For example, U.S. Pat. No. 3,947,525 to Robertson et al. discloses a melt-processable, radiation cross-linkable ethylene/chlorotrifluoroethylene type coating composition which, when coated on a substrate in the presence of radiation provides a high tensile strength stress-crack resistant coating.